1. Field of the Invention
The invention relates to the field of earth boring tools and more particularly to hydraulic nozzles which may be threadably inserted and replaced in rotating bits which are manufactured using powder metallurgical infiltration techniques.
2. Description of the Prior Art
A rotating drill bit is cooled and cleaned by drilling mud provided to the bit surface during the normal drilling operation. In some cases, the drilling mud is provided axially or through the bit face through a plurality of off-center crowfoot openings in the bit, each of which communicate with an axial bore defined in the bit to which drilling mud is supplied. The drilling mud flows out the crowfoot openings provided through the bit, flows across the bit surface up its gage and junk slots, and thence upwardly along the drill string carrying chips, debris and junk away from the drilling surface.
In certain applications, to obtain a directed flow or to provide high velocity jets of drilling fluid, the crowfoot openings may be replaced by one or more replaceable jet nozzles which are either molded into the steel drilling bit or may be inserted therein such as by means of a snap-ring retaining element. A jet nozzle has a specially formed orifice designed according to well understood principles to concentrate the drilling mud and to form a high velocity and directed output. In the case of steel bits, it is usually easiest and most economical to machine a threaded bore in the bit into which a nozzle may be threaded. Alternatively, a snap-ring retaining groove is machined in a drilled bore into which the replaceable nozzle is inserted and which is then retained by a retaining ring engaging the groove to prevent the nozzle from being blown out by the high pressure drilling mud.
However, it is not possible to practically manufacture a drilling bit incorporating diamond cutting elements in a steel bit. Typically, diamond bits are manufactured by powder metallurgical techniques using a tungsten carbide matrix. A conventional process is used wherein the bit is molded and the desired constituents of the matrix are infiltrated through the tungsten carbide powder during a furnacing step. However, such tungsten carbide material, although it is extremely hard and abrasive resistant, is highly brittle. Because of the hardness of the material, it becomes practically impossible to machine the material or to drill bores therethrough. In addition, because of the brittleness of the material, threads or other fine structures which may be molded into a tungsten carbide drilling bit thus formed, have insufficient strength to provide a secure attachment for threaded nozzles inserted into the bit. As a result, the threads tend to fail and the nozzles are eventually blown out of the bit when the means for their retention therein is lost. The drilling fluid entering the nozzle tends to erode the matrix material forming the bit about the entry point of the nozzle and therefore tends to erode the threads formed into the bit material. After sufficient erosion of the threads, the nozzle will be blown out from the bit.
Therefore, what is needed is a method whereby replaceable nozzles may be inserted and retained into a tungsten carbide bit without being subject to the foregoing disadvantages.